Various forums and logging sites around the web have reported that short-wave pirate station Premier Radio International was recently raided. Their transmitters and studio equipment were apparently taken. Premier Radio operated on 6265 kHz on Sunday mornings from Ireland and according to the reports the Irish spectrum regulator, ComReg, received a complaint of interference from the UK spectrum regulator Ofcom which forced them into action.

Such a raid on pirate broadcasters is not unheard of, though a 'cease and desist' letter is often sent to the operator first to warn them that they are at risk of being 'boarded'. Short-wave stations, however, are raided much less frequently than their FM pirate counterparts who lose transmitters on a regular basis. One of the reasons for this is that it can be much more difficult to identify the location of a short-wave transmitter. The other is that interference tends to be caused outside the country in which the transmitter is located - hence the need for the collaboration between Ofcom and ComReg.

There are, however, many short-wave pirate stations that operate in and around 6200 to 6400 kHz on Sunday mornings, and many of them operate from Ireland. So the question is, what is it about the use of this frequency that Ofcom found so objectionable that they felt the need to get ComReg to take such drastic action.

The answer might lie in the particular use of frequency in that part of the radio spectrum. Frequencies from 6200 to 6525 kHz are allocated internationally to maritime mobile services. Within this range, certain spot frequencies have been set aside at an international level, through the International Telecommunications Union (ITU) Radio Regulations for certain specific uses. These frequencies are:

Clearly, given the safety related nature of the use of these frequencies, it makes sense to avoid them as far as possible to avoid causing interference where it really is not welcome. However, avoiding them does not just mean not transmitting on those spot frequencies. Typical AM transmitters occupy 5 kHz either side of the centre frequency on which they are transmitting. Also the spot frequencies themselves refer to transmissions with typically a 2 or 3 kHz bandwidth. So, to avoid interfering with 6215 kHz which actually uses frequencies from 6215 to 6218 kHz for example, AM transmissions on a centre frequency ranging from 6210 to 6223 kHz should be avoided. This might immediately raise the question as to why Ofcom have not complained about Italy's Mystery Radio who have used 6220 kHz for a very long time or Radio Cairo which uses 6270 kHz between 16:00 and 18:00 GMT every day, but certainly gives credence to claims that Radio Caroline's use of 6215 kHz in the late 1980s could have caused interference to safety-of-life services. With this in mind, the diagram below illustrates which frequencies within the range 6200 to 6400 kHz can be 'safely' used (in blue) without causing interference to these safety related services.

Interfering with any legitimate radio user is not to be condoned, however safety services such as these are not the best of bedfellows. I am sure that many pirates listen to the frequency they intend to use before turning their transmitters on, assuming, that is, that they have sufficient flexibility in their choice of crystals to allow them to find something relatively free. Choosing a frequency that deliberately interferes is, though, clearly a bit mad. So Radio King on 6215 kHz, Radio Malaisy on 6310 kHz and Radio Altrex who use both 6265 and 6310 kHz - be warned - you might be next to be sunk.

Whilst we're on the subject of frequencies not to choose, much of the HF spectrum is littered with transmissions that sound like this. These are NATO transmissions using their HF radio protocol known as STANAG 4285 and are therefore most definitely military in nature. Avoiding any frequency on which these noises can be heard would also seem to make sense too... otherwise it might be torpedos away.

Further to last month's comments on receiving BBC World Service English in Europe, we've been testing out some of the frequencies that were suggested from the Wireless Waffle HQ in southern Great Britain. At all times checked, at least one BBC English frequency was available and at some times, several were audible. The list below gives the times checked and the frequencies that were audible. A simple rating system has been employed with one * representing poor reception, ** representing reasonable reception and *** representing a nice strong signal.

Reception will change from day-to-day and month-to-month so this list may not remain accurate indefinitely but it shows what can be achieved with a little effort. This list will be updated from time-to-time so check back occasionally if you're missing your Lily Bolero!

The end of an era is afoot (or at hand, whichever you prefer). Earlier this year the BBC World Service announced that it has stopped transmission of its English service to Western Europe. No longer will the strains of 'Lili Bolero' or 'Big Ben' be heard on the hour in France, Germany or anywhere east of Moscow. Or will it?

The BBC claim that certain frequencies destined for other parts of the world, notably Western Russia, may still be audible in some parts of Europe for those who absolutely insist on listening to the news from London with loads of hiss, crackle, distortion and fading. But to what extent is this possible? Is World Service short wave reception in Western Europe gone forever or is there still the possibility to listen in?

A scan of the material published by the BBC shows that there are still plenty of transmitters on-air carrying BBC World Service English (albeit different regional variants), pretty much around the clock. The question therefore is whether any of them are audible in Europe.

Whether or not a short wave transmission is audible in any given place depends on a number of factors including the transmission frequency, the time of day (in particular whether the path between transmitter and receiver is in daylight or darkness), the distance between transmitter and receiver and the intended target for the transmission. Take for example the World Service English transmission to Africa from its transmitter site on Ascension Island in the South Atlantic. At various times during the (European) day, this is on a frequency of 17830 kHz. This high frequency propagates well through areas in daylight and the direction of the transmission is roughly the same as the direction from Ascension to most of Europe. The distance between Ascension and Europe requires the transmission to hop into and out of the ionosphere a couple of times but on a normal day, if both ends of the path are in daylight, this should work. Barring any co-channel or strong adjacent channel interference, therefore, the BBC transmission from Ascension should be (and indeed is) audible in Europe.

During the hours of darkness, low frequencies (the 48, 41 and 31 metre band for example) tend to propagate well, whereas during the day, higher frequencies (the 25, 19 and 16 metre bands) will fare better. Taking all this into account, it should be possible to construct a schedule of which BBC World Service English programmes are most likely to be heard in Europe. Of course this will change twice a year as the winter and summer schedules take effect, but the principles should hold true.

With that in mind, here is the Wireless Waffle guide to receiving BBC World Service English in Europe on short wave. The frequencies shown are those that have the best chance of being received in Europe but which are directed to other regions (thus the programming material may not necessarily be appropriate). No account of possible interference has been made (for example it is known that the BBC frequency of 17640 kHz suffers strong adjacent channel interference in Europe from Africa No. 1 on 17630 kHz and China Radio International on 17650 kHz). Other frequencies have strong co-channel and adjacent channel interference too so it's definitely a case of 'if at first you don't succeed, try, try, try again'.

Note that these frequencies were taken from the Winter 2008/9 broadcast schedule and may be very out of date if you are reading this in 2013! Also, not all frequencies are on for the whole period (some are not daily either), so you will have to tune around between the ones listed to find the best possible reception for the time you are listening.

It may appear to have been quiet here at Wireless Waffle over the past couple of months, but that's because a number of things have piqued the interest and we've been doing a bit of experimentation and investigation. The first of them is the issue of Power Line Telecommunications (PLT) also known as Broadband over Power Line (BPL) and in particular the problems being experienced by many UK short-wave radio listeners with it. One of these devices could recently be heard, albeit quietly, across the HF spectrum (oddly it has since disappeared) at Waffle HQ but it raised the question as to how many more there were in the area. To find out, I fitted and HF antenna to my car and connected it to an HF receiver and then drove around a nearby housing estate to see what could be heard.

The antenna used resonated in the 18 MHz (17 metre) amateur band but received perfectly well in the 17 MHz (16 metre) broadcast band. Tuned to a clear channel around 17460 kHz, the car was driven around the area under test. Over the area covered by a small local estate, three devices were detected. Two were almost certainly the 'Comtrend' device, sounding just as the ones that UKQRM has demonstrated on YouTube. The third (shown in red on the map) emitted a more continuous tone, interrupted by occasional blips; the range of this device was somewhat less than the other two. Their range at other frequencies was not tested but anecdotal evidence driving round the area using other antennas and the same receiver suggests that the coverage on frequencies around 27 MHz is similar.

I've plotted the approximate location of the three devices identified together with the area over which they were clearly receiveable on the map on the right (the map covers approximately a 500 metre by 500 metre area). The blue device had the largest interference range and within the areas marked it is unlikely that any short-wave reception would be possible.

The density of these devices means that over the whole estate, short-wave reception would be virtually impossible. A cursory glance around the area indicated no amateur radio antennas so it is likely the devices are going undetected (or just unreported!) Not a positive result and unless the powers that be do something to halt the spread of these devices, it would be easy to foresee a situation where HF reception could be pretty much impossible over whole towns and cities, in residential areas for certain.

One piece of positive news is that Ofcom have set up a special team to deal with PLT interference and appear to have begun taking the problem seriously. Let's hope that this is more than just paying lip service to the problem before the whole HF spectrum is lost to the laziness of those who can't be bothered to use WiFi or put a piece of wire between various bits of equipment in their home. These devices are a disgrace and a menace and before they wipe out all short-wave reception and neighbour-on-neighbour war breaks out, serious action by the authorities is absolutely necessary.